I've never heard the term substantive pronoun... seems kind of redundant. "Substantive" is usually used to describe a word that is not a noun but is functioning as one. IPSE is the intensive pronoun and it usually functions like an adjective, meaning it stands next to a noun and agrees with it in case, number, gender. IPSE can, however, stand alone if it's antecedent is in the verb.. for instance: id ipse timeo. - "I myself fear it."

Here ipse is not a substantive pronoun, it is an adjectival pronoun (an intensive adjectival pronoun),â€”as an adjective, it qualifies a noun. In your sentence, it qualifies the substantive pronoun "we".